Los Frailes Aftermath

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The Aftermath
The initial action taken by Boliden was to fill the 50 m breach in the tailings impoundment embankment with waste rock and clay, to prevent any further release of tailings. The section of the embankment that failed is also being supported by the construction of a buttress layer of clay on the outer edge.

According to data provided by both Boliden and the Spanish authorities, the pH level in the upper section of the Rio Guadiamar had returned to normal (about 7) within ten days of the disaster. However, although the total zinc levels decreased rapidly during the first ten days, they are still elevated and are expected to stay this way until the clean-up operation has been completed. It has been decided that no action will be taken to clean up the actual rivers and that it is safer to leave this to natural processes. The latest monitoring data available from the government shows that the total zinc levels in mid-June, in the Entremuros were 94.3 ppm, although the pH was reading 7.3.

Following negotiations between the company and the government, it was agreed that the clean-up of the inundated areas along the banks of the rivers would be divided into three sections. Boliden would be responsible for the first section, from the tailings impoundment to the Sanlúcar la Mayor bridge, including the Rio Agrio and Rio Guadiamar, while the government would be responsible for the other two sections from the Sanlúcar la Mayor bridge down to the southern end of the Entremuros. In addition, Boliden has obtained a permit from the government for the disposal of the tailings, removed during the clean-up operations, into the Aznalcóllar open pit.

The clean-up officially started on May 3, and it is estimated that a total of 3 million m³ of tailings and contaminated topsoil will have to be removed from Section 1 alone. The aim is to complete the removal of material by the end of September, before the rains start in October. In the badly inundated areas the plan is to scrape the surface off, removing the tailings, topsoil and any vegetation except for the larger trees which can be saved. This is being done with bulldozers and mechanical diggers, and the material is loaded into lorries and taken to the Aznalcóllar open pit for disposal. The rate of clean-up is approximately 20,000 m³/d and, by June 22, a total of 750,000 m³ had been removed, with 684,000 m³ from Section 1, 42,800 m³ from Section 2 and 22,800 m³ from Section 3.

In addition to the physical clean-up, both the government and Boliden have instigated detailed investigation programmes and established various committees. The government has set up an internal commission, which includes both the central and the regional government, to co-ordinate the handling of the disaster and to investigate the causes. A technical committee has also been established, to report to the commission, and it has secured the services of two experts to advise the commission, one toxicology specialist and one water specialist. The government is also carrying out a number of monitoring exercises which include water quality analysis for the rivers and wells, and soil sampling from all the inundated areas.

The government is also looking at alternatives for treating and discharging the water from the Entremuros area into the Rio Guadalquivir. The options being investigated include filtering the water before discharge or using a bioremediation system in situ to remove the heavy metals from the water before it is released. A consortium of North American and South African companies has been invited by the government to submit a proposal and carry out on-site demonstrations of methods for treating the water. The consortium is looking at the possibility of using high-pressure water cannons to hydrosluice the contaminated areas upstream that cannot be cleaned with mechanical equipment, and then using bacterial stabilisation to purify the water prior to its release.

Independently Boliden has established three main project teams to work on various aspects of the investigation project.

Environmental Impact Assessment and Reclamation Planning
The programme, headed by Manfred Lindvall, has been set up to look at the impacts of the tailings on the environment and to establish methods for rehabilitating the contaminated areas. As well as including internal experts, this team will also include an independent expert panel made up of a range of specialists, with external quality control provided by the consultant company, Micon. The work includes a new monitoring programme for the Guadiamar and Guadalquivir river systems, which started on June 6; it is changing the monitoring from total metals to dissolved. This programme will incorporate new technologies that will provide a more accurate analysis of the trace elements and heavy metals in the saline and semi-saline waters that are found in the tidal areas in the lower reaches of the river. Fish have already returned to the Rio Guadiamar and a consulting company, hired by Boliden, is taking samples, looking for any indication of elevated levels of heavy metals.

Independent Assessment of the Failure
EPTISA, which specialises in dam design, mine engineering and environmental studies, has been commissioned to carry out an independent investigation into the failure of the embankment. The work will involve more than 1,000 m of drilling, geological investigations and a study of the materials used in, and found around, the dam. The report is due to be completed by mid-September. A panel of independent engineering experts from Spain, Sweden and Canada will review the final report.

Future Tailings Disposal Options
Golder Associates, in association with Aurenca, a Spanish environmental consulting company, has been retained to investigate the future options for the project with respect to waste disposal and rehabilitation. Golder’s first task is to look at the options for tailings disposal in order to facilitate the re-opening of the project as soon as possible. The most favoured option at this stage is the disposal of the tailings in the old Aznalcóllar open pit. However, the Los Frailes project was originally permitted with the open pit being used only for the disposal of waste rock, and there is insufficient space for both types of waste. Therefore, Golder has also been asked to look for alternative options for disposing of the waste rock. In addition, the consultants have been requested to establish a method for closing and rehabilitating the old tailings impoundment. Golder had previously conducted a hydrogeological study of the water seepage from the tailings impoundment and surrounding areas.

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